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Scania CV AB 2011, Sweden
83
Closed crankcase
ventilation
Troubleshooting
Increased blow-by in engine
Blow-by is the flow of gases through the engine
crankcase and out via the crankcase ventilation.
The closed crankcase ventilation system is very
sensitive to changes in blow-by in the engine. If
the blow-by increases, the amount of gas
passing through the crankcase ventilation will
also increase. The crankcase gases can then take
with them small drops of oil from the crankcase.
When the amount of oil increases, the oil
separator will not be able to fulfil its task of
separating out all the oil. Oil will then
accompany the air into the charge air system.
Causes of an increase in blow-by are leaking
piston rings, valve guides, turbocharger or
compressor. Gas leakage from the charge air
system down to the crankcase also gives rise to
increased blow-by and therefore increased oil
carryover from the crankcase ventilation.
Too much oil in the oil sump
If the engine is filled with too much oil, the
excess will splash around in the crankcase and
be atomised. This means that the crankcase
gases will contain a large amount of atomised
oil and that the crankcase ventilation will not be
able to separate the oil properly. This will result
in a large oil carryover from the crankcase
ventilation.
Closed crankcase ventilation
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